Corrosion inhibiting compositions and process



$347,510 Patented July 31, 1962 This invention relates to new corrosion inhibitor compositions. In one of its aspects, this invention relates to corrosion resisting acid solutions useful in the cleaning of metallic surfaces. in another of its aspects, this invention relates to an improvement in the cleaning of metallic surfaces employing aqueous acid solutions.

In steel mills aqueous acid solutions are used to pickle iron and steel. That is, in the process of manufacturing, metal is worked at elevated temperatures and on cooling it becomes coated with a layer of oxide, generally called scale or mill scale. The process of removing scale and rust using dilute aqueous acid solutions is known as pickling. Most worked metal which is to be coated, plated or processed through a die, is first pickled. Because of its price, availability and ability to perform an efiicient job, sulfuric acid is used quite extensively in pickling, although sulfamic, phosphoric and other acids are also employed. Acid solutions are also commonly used in the cleaning of other metal surfaces such as Zinc, aluminum, brass and the like.

In the cleaning of metal surfaces with acid solutions after the scale and other undesirable surface impurities are dissolved, the acid is free to corrode or dissolve the exposed metal surface. For example, the corrosion rate of mild steel in 15%, by weight, sulfuric acid at 200 F. is over 2.5 pounds per square foot per day. Thus, for every pound of iron dissolved, about 2.5 pounds of 60 Baumm sulfuric acid are spent and nearly 7 cubic feet of hydrogen gas are evolved. In view of this, it is common for pickling baths to contain an acid corrosion inhibitor. These inhibitors must not retard the pickling efficiency of the acid, and should also reduce acid fuming and spattering into the atmosphere. A common deficiency in commercially available pickling bath inhibitors is the deposit of a resinous film on the surface of the metal which tends to color the same and interfere with subsequent cleaning and coating operations. Also, many of the available inhibitors are difiicult to work with by reason of their physical form and their slight solubility in the pickling bath.

In accordance with the present invention, I have found that a synergistic corrosion inhibiting effect is produced by combining in a particular proportion two agents which by themselves are not particularly effective as corrosion inhibitors. These mixtures are easily handled, being liquid and soluble at ordinary temperatures, and leave the cleansed surface free of any undesirable resinous film. Also, these mixtures are particularly efiective corrosion inhibitors in sulfuric, sulfamic and phosphoric acid solutions.

It is, therefore, an object of this invention to provide new corrosion inhibitor compositions.

It is another object of this invention to provide corrosion resisting acid solutions useful for the cleaning of metallic surfaces.

It is still another object of this invention to provide an improved process for the cleaning of metallic surfaces employing aqueous acid solutions.

My improved corrosion inhibiting composition contains one part of dibutylthiourea and from 1 to parts by weight of a quaternary ammonium compound represented by the formula R NX wherein R is an aliphatic hydrocarbon radical having from 1 to 22 carbon atoms, said compound being further characterized by the fact that at least 1 and no more than 2 of the Rs is an aliphatic hydrocarbon radical containiug from 8 to 22 carbon atoms, and X is a halide such as chlorine or bromine. The preferred ratio of dibutylthiourea to quaternary ammonium compound is l to 3 parts by weight.

7 Examples of long chain aliphatic hydrocarbon radicals having from 8 to 22 carbon atoms coming within the definition of R described hereinabove include octyl, decyl, dodecyl, tetradecyl, hexadecyl, octadecyl, octadecenyl, octadecadienyl, octadecatrienyl, docosyl, eicosyl, and mixtures of the foregoing hydrocarbon radicals as contained in naturally occurring glycerides such as coconut oil, tallow, soybean oil, and the like. For example, coconut oil contains a mixture comprising approximately by weight 5% octadecenyl, 5% octadecyl, 8% hexadecyl, 18% tetradecyl, 47% dodecyl, 9% decyl, and 8% octyl radicals; tallow contains a mixture comprising approximately by weight 45% octadecenyl, 30% octadecyl, and 25% hexadecyl radicals; soybean oil contains a mixture comprising approximately by weight 37% octadecadienyl, 26% octadecenyl, 17% octadecyl, and 20% hexadecyl radicals.

Examples of short chain aliphatic hydrocarbon radicals coming within the definition of R as described hereinabove include methyl, ethyl, propyl, butyl, and pentyl radicals.

Examples of preferred mixtures useful in accordance with the present invention include three parts by weight of tallowtrimcthylammonium chloride per part of dibutylthiourea; 3 parts by weight of cocotrimethylammonium chloride per part of dibutylthiourea; 3 parts by weight of dicocodimethylammonium chloride per part of dibutylthiourea; 3 parts by weight of ditallowdimethylammonium chloride per part of dibutylthiourea; and 3 parts by weight of dodecyltrimethylammonium chloride per part of dibutylthiourea. These mixtures can be prepared by simple mixing of the ingredients in the proper proportions.

In the practice of the present invention, the mixture of dibutylthiourea and quaternary ammonium compound can be incorporated directly into the aqueous acid solution in a concentration by weight of from about 0.1 to 1.0, preferably about 0.2 to about 0.5 percent, based upon the acid concentration, and the resulting aqueous acid solution used in the conventional manner in pickling and metal cleaning processes. Alternatively, the mixture can be incorporated, at the same concentration level described, into a concentrated acid, which is then diluted before use. There is little or no adverse effect upon the corrosion inhibiting properties of the acid under these circumstances, even after a period of storage.

The following Example will help to illustrate the underlying principles of my invention, and is not to be construed as unduly limiting:

Example I Test cells containing small quantities of dilute acid, both inhibited and uninhibited were prepared. The concentnation of the acid was on a weight basis, and the percent inhibitor used was based on the acid concentration. The acid solutions were pre-heated to the desired temperature and held at i2 F. Clean, weighed mild steel coupons were exposed to the acid for 6 hours. At the end of this period the coupons were washed free of acid and salts, dried, and reweighed. The corrosion rate was calculated in pound per square foot per day. Visual observations were made for discoloration and pitting of the coupons. The results of these tests are set forth in Table I.

TABLE I Percent Chemical Percent inhib' Acid acid itor Coupon Corr. rate, Coupon Corr. rate, Fitting 1 color 2 lbs/sq. it./ Pitting 1 color 1 lbs/sq. it./

day day 1. Cocotriinethylammonium chloride.... 10 0. 2 H2804 Slight Light..- 0. 034 0.112 2. Cocotrimethylarnmonium chloride 10 0. 3 ....do.. d 0.022 0.055 3. Cocotrilncthylamrnonium chloride. 10 0.75 Excellen 0.029 4. Tallowtrimethylammonium chloride- 10 0. 3 Slight 0. 095 Tallowtrimethylammonium chloride 10 0. 5 Very slight. 0.075 5. Dibytyl thiourea O. 3 Excellent... 0. 040 6. Dibytyl thiourca.. 10 0.75 Excellent.... 0. 014 7. Control 10 Even Even Black... 2. 8. Coctrirnethylammonium chloride, 10 0. 2 Excellent.... Light..- 0.007 Very slight.. Light..- 0.011

75%; dibutyl thiourea, 9. Dibutyl thiourea 10 0. 3 Excellent.... 0.010 10. Dibutyl thiourea-.. 10 0.75 d 0.010 11. Tnllo\vtrirnethylammoniurn chloride 10 0.30 0.022

75%; dibutyl thiourea, 25%. 12. Dibutyl thiourea 10 0.75 0.011 13. Cocotrimethylammoniurn chloride---.- 15 0.20 0. 195 14. Cocotrimethylammonium chloride. 15 0.20 15. Cocotrirnethylammoniurn chloride-... 15 0.50 0.044 16. Tallowtrirnethylammonium chloride- 15 0. 0.194 17. Tallowtrimethylammonium chloride.. 15 0. Very slight. ..--.do. 0. 086 18. Dibutyl thiourea.. 15 0.30 Excellent.... .0 Slight ..do 0.056 19. Dibutyl thiourea... 15 0.50 d Excellent.... Light. 0.028 20. Cocotrimethylarnmo ch 15 0. 2 Very slight.. .....do 0.016

75%; dibutyl thiourea, 25%. 21. Dibutyl thiourea 15 0. 3 --...do .do 0.017 22. Dibutyl thiourca. 15 0. 5 23. Dibutyl thiourea... 15 0.75 Very slight. Light... 0.011 24. Tallowtrimcthylammonium chloride, 15 0. 5 Excellent... ..-..do 0.036

75%; dibutyl thiourea, 25%. 25 Control 15 HzSO4 Even Block... 0. 502 Even Bloc 2.53

1. Cocotrimethylammonium chloride, 10 0. 2 H3PO4.

75%; dibutyl thiourea, 25%. 2. Dibutyl thiourea l0 0. 4 H3PO4 3. Dibutyl thiourea. 15 0. 2 H POr 4. Dibutyl thiourea. 15 0. 4 H31 0; 5. Control 15 HgPOr 1. Cocotrimethylamrnonium chloride, 10 0.2 NII2SO3iI 0.003 Slight Light... 0.032

75%; dibutyl thiourea, 25%. 2. Dibutyl thiourea 10 0.3 NHQSOaH... 0.002 Excellent... o.-. 0.013 3. Control 10 Nl'lzSOfl-I... 0.126 Even Black... 0. 892

l Fitting: 1. EvenThe entire surface and edges of metal are pitted. or metal is clean and edges are pitted.

2. Slight-Evensurface and edges have a few pit marks. 4. Slight-Suriace of metal is clean and edges for the most part are pitted. 5. Very slightSuriace of 3. EdgesSnrIace metal is clean and edges have only slight indications of being pitted. 6. Excellent-No trace of pitting detected.

Coupon color: 1. BlackSelf explanatory. 2. Tint-Surface of metal is slightly discolored. 3. Light-Clean surface, no indication of discoloration While the present invention has been described and exemplified in terms of preferred embodiments, those skilled in the art will appreciate that variations can be made without departing from the spirit and scope of the invention.

I claim:

1. As a new corrosion inhibiting composition a synergistic combination of about 1 part by weight of dibutylthiourea and from 1 to 5 parts by weight of a quaternary ammonium compound represented by the formula R NX wherein X is a halide and R is an aliphatic hydrocarbon nadical containing from 1 to 22 carbon atoms, and further characterized by the fact that said quaternary ammonium compound contains at least 1 and no more than 2 long chain aliphatic hydrocarbon radicals having from 8 to 22 carbon atoms.

2. As a new corrosion inhibiting composition a synergistic combination of 1 part by weight of dibutylthiourea and 3 parts by weight of cocotrimethylammonium chloride.

3. As a new corrosion inhibiting composition a synergistic combination of 1 part by weight of dibutylthiourea and 3 parts by weight of tallowtrimethylammonium chloride.

4. A composition substantially non-corrosive to metals comprising an aqueous solution of an acid selected from the group consisting of sulfuric, sulfamic and phosphoric acids, and from 0.1 to 1.0 weight percent, based on the acid, of a corrosion inhibiting synergistic combination of about 1 part by weight of dibutylthiourea and from 1 to 5 parts by weight of a quaternary ammonium compound having the formula R NX wherein X is a halide and R is an aliphatic hydrocarbon radical containing from 1 to 22 carbon atoms, and further characterized by the presence of at least 1 and no more than 2 aliphatic hydrocarbon radicals containing from 8 to 22 carbon atoms.

5. A composition substantially non-corrosive to metals comprising an aqueous solution of an acid selected from the group consisting of sulfuric, sulfamic, and phosphoric acids, and from 0.1 to 1.0 weight percent, based on the acid, of a corrosion inhibiting synergistic combination of 1 part by weight of dibutylthiourea and 3 parts by weight of cocotrimethyiammonium chloride.

6. A composition substantially non-corrosive to metals comprising an aqueous solution of an acid selected from the group consisting of sulfuric, sulfamic, and phosphoric acids, and from 0.1 to 1.0 weight percent, based on the acid of a corrosion inhibiting synergistic combination of 1 part by weight of dibutylthiourea and 3 parts by weight of tallowtrimethylammonium chloride.

7. A composition substantially non-corrosive to metals comprising an aqueous solution of sulfuric acid containing from about 0.2 to about 0.5 weight percent, based on the sulfuric acid, of a corrosion inhibiting synergistic combination of 1 part by weight of dibutylthiourea and 3 parts by weight of cocotrimethylammonium chloride.

8. A composition substantially noncorrosive to metals comprising an aqueous solution of sulfuric acid containing from about 0.2 to about 0.5 weight percent, based upon the sulfuric acid, of a corrosion inhibiting synergistic combination of 1 part by weight of dibutylthiourea and 3 parts by Weight of tallowtrirnethylammonium chloride.

9. In a process wherein metal surfaces are cleaned through the action of a dilute aqueous solution of an acid selected from the group consisting of sulfuric, sulfamic and phosphoric acids, the improvement comprising having in said acid solution from about 0.1 to about 1.0 weight percent, based on the concentration of acid, of a corrosion inhibiting synergistic combination of about 1 part by weight of dibutylthiourea and from 1 to 5 parts by weight of a quaternary ammonium compound having the formula R NX wherein X is a halide and R is an aliphatic hydrocarbon radical containing from 1 to 22 carbon atoms, and further characterized by the presence of 5 at least 1 and no more than 2 aliphatic hydrocarbon radicals containing from 8 to 22 carbon atoms.

10. In a process wherein metal surfaces are cleaned through the action of a dilute aqueous solution of an acid selected from the group consisting of sulfuric, sulfamic, and phosphoric acids, the improvement comprising having present in said solution from about 0.1 to about 1.0 Weight percent, based on the concentration of the acid, of a corrosion inhibiting synergistic combination of 1 part by weight of dibutylthiourea and 3 parts by Weight of cocotrimethylamrnonium chloride.

11. In a process wherein metal surfaces are cleaned through the action of a dilute aqueous solution of an acid selected from the group consisting of sulfuric, sulfamic, and phosphoric acids, the improvement comprising having present in said solution from about 0.1 to about 1.0 weight percent, based on the concentration of the acid, of a corrosion inhibiting synergistic combination of 1 part by Weight of dibutylthiourea and 3 parts by weight of tallowtrimethylarnmonium chloride.

12. In a process wherein metal surfaces are cleaned through the action of a dilute aqueous solution of sulfuric acid, the improvement comprising having present in said sulfuric acid solution from about 0.2 to about 0.5 weight percent, based on the concentration of the sulfuric acid,

6 of a corrosion inhibiting synergistic combination of 1 part by weight of dibutylthiourea and 3 parts by weight of cocotrimethylammonium chloride.

13. In a process wherein metal surfaces are cleaned through the action of a dilute aqueous solution of sulfuric acid, the improvement comprising having present in said sulfuric acid solution from about 0.2 to about 0.5 weight percent, based on the concentration of the sulfuric acid, of a corrosion inhibiting synergistic combination of 1 part by Weight of dibutylthiourea and 3 parts by weight of tallowtrimethylammoniurn chloride.

References Cited in the file of this patent UNITED STATES PATENTS 1,678,775 Gravell July 31, 1928 1,736,118 Gravell Nov. 19, 1929 2,006,216 MacArthur et al June 25, 1935 2,461,228 Miles Feb. 8, 1949 2,485,529 Cardwell et al. Oct. 18, 1949 2,585,127 Holman et al. Feb. 12, 1952 2,617,771 Rucker Nov. 11, 1952 2,628,199 Lowenheim Feb. 10, 1953 2,662,857 Carroll Dec. 15, 1953 2,713,033 Cardwell et al July 12, 1955 2,728,727 Marsh Dec. 27, 1955 2,759,975 Chiddix et a1. Aug. 21, 1956 2,947,703 Larsonneur Aug. 2, 1960 FOREIGN PATENTS 732,834 Germany Mar. 12, 1943 

4. A COMPOSITION SUBSTANTIALLY NON-CORROSIVE TO METALS COMPRISING AN AQUEOUS SOLUTION OF AN ACID SELECTED FROM THE GROUP CONSISTING OF SULFURIC, SULFAMIC ANDF PHOSPHORIC ACIDS, AND FROM 0.1 TO 1.0 WEIGHT PERCENT, BASED ON THE ACID, OF A CORROSION INHIBITING SYNERGISTIC COMBINATION OF ABOUT 1 PART BY WEIGHT OF DIBUTYLTHIOUREA AND FROM 1 TO 5 PARTS BY WEIGHT OF A QUATERNARY AMMONIUM COMPOUND HAVING THE FORMULA R4NX WHEREIN X IS A HALIDE AND R IS AN ALIPHATIC HYDROCARBON RDICAL CONTAINING FROM 1 TO 22 CARBOAN ATOMS, AND FUTHER CHARACTERIZED BY THE PRESENCE OF AT LEAST 1 AND NO MORE THAN 2 ALIPHATIC HYDROCARBON RADICALS CONTAINING FROM 8 TO 22 CARBON ATOMS. 